darwin: support Boehm GC (and use by default)

This mostly required some updates to macos-minimal-sdk to add the needed
header files and symbols.

Author: aykevl

builder/ar.go

@@ -3,6 +3,7 @@ package builder
 import (
 	"bytes"
 	"debug/elf"
+	"debug/macho"
 	"debug/pe"
 	"encoding/binary"
 	"errors"
@@ -62,6 +63,20 @@ func makeArchive(arfile *os.File, objs []string) error {
 					fileIndex int
 				}{symbol.Name, i})
 			}
+		} else if dbg, err := macho.NewFile(objfile); err == nil {
+			for _, symbol := range dbg.Symtab.Syms {
+				// See mach-o/nlist.h
+				if symbol.Type&0x0e != 0xe { // (symbol.Type & N_TYPE) != N_SECT
+					continue // undefined symbol
+				}
+				if symbol.Type&0x01 == 0 { // (symbol.Type & N_EXT) == 0
+					continue // internal symbol (static, etc)
+				}
+				symbolTable = append(symbolTable, struct {
+					name      string
+					fileIndex int
+				}{symbol.Name, i})
+			}
 		} else if dbg, err := pe.NewFile(objfile); err == nil {
 			for _, symbol := range dbg.Symbols {
 				if symbol.StorageClass != 2 {

builder/bdwgc.go

@@ -24,6 +24,7 @@ var BoehmGC = Library{
 			"-DALL_INTERIOR_POINTERS",  // scan interior pointers (needed for Go)
 			"-DIGNORE_DYNAMIC_LOADING", // we don't support dynamic loading at the moment
 			"-DNO_GETCONTEXT",          // musl doesn't support getcontext()
+			"-DGC_DISABLE_INCREMENTAL", // don't mess with SIGSEGV and such
 
 			// Special flag to work around the lack of __data_start in ld.lld.
 			// TODO: try to fix this in LLVM/lld directly so we don't have to
@@ -63,8 +64,6 @@ var BoehmGC = Library{
 			"new_hblk.c",
 			"obj_map.c",
 			"os_dep.c",
-			"pthread_stop_world.c",
-			"pthread_support.c",
 			"reclaim.c",
 		}, nil
 	},

builder/build.go

@@ -150,8 +150,8 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	var libcJob *compileJob
 	switch config.Target.Libc {
 	case "darwin-libSystem":
-		job := makeDarwinLibSystemJob(config, tmpdir)
-		libcDependencies = append(libcDependencies, job)
+		libcJob = makeDarwinLibSystemJob(config, tmpdir)
+		libcDependencies = append(libcDependencies, libcJob)
 	case "musl":
 		var unlock func()
 		libcJob, unlock, err = libMusl.load(config, tmpdir, nil)

compileopts/target.go

@@ -380,7 +380,7 @@ func defaultTarget(options *Options) (*TargetSpec, error) {
 	llvmvendor := "unknown"
 	switch options.GOOS {
 	case "darwin":
-		spec.GC = "precise"
+		spec.GC = "boehm"
 		platformVersion := "10.12.0"
 		if options.GOARCH == "arm64" {
 			platformVersion = "11.0.0" // first macosx platform with arm64 support